1. Field of Disclosure
The present invention relates to the dispensing of media and, more specifically, to the verification of dispense operations.
2. Description of Related Art
In various fields there is a need for accurate dispensing of gases, fluids, and slurries (collectively, “media”). Often the dispensing is repetitive. For example, in the semiconductor industry, the manufacture of silicon chips involves multiple complex processing steps where various media are applied to semiconductor wafers to perform various tasks such as photomasking, etching, polishing, cleaning, and chemically modifying the wafers. These processing steps depend on dispensing accurate volumes of the media. As another example, in the biopharmaceutical industry, the manufacture of drugs and test products (e.g., blood test strips) frequently requires dispensing accurate volumes of media.
Dispense pumps are frequently used to control accurate dispensing of media. For example, one can control the dispense operation of a diaphragm pump by controlling the distance that the pump's diaphragm moves and the precise opening and closing time of the pump's valves. However, accurate control of the pump alone may not necessarily lead to accurate dispensing. Other factors also affect the dispense accuracy of a pump system. For example, pump systems are susceptible to various characteristics of the surrounding environment that can modify how much media is actually dispensed. These environmental factors include the pressure of the media at the inlet side of the pump, the accuracy of the timing signals used to control the pump's operation, the pressure of the environment in to which the media is dispensed, the viscosity of the media being dispensed, and the resistance to media flow of the tubing used on both the inlet and outlet side of the pump. Dispense systems may also behave unreliably if there are bubbles in the media, if there are blockages in the system, or if the source media is all consumed (e.g., the source vessel runs empty). Another factor that may affect the accuracy of dispense pumps is that contaminants in the media may damage the valve surfaces, or interfere with the correct opening and closing of the valves. In addition, dispense pumps are usually unable to verify that the correct volume is delivered under the various situations where environmental factors interfere with accurate delivery.
Similar to dispense pumps, the accuracy of systems and devices used to measure volumes or flow rates of media is also susceptible to environmental factors such as the temperature and pressure of the media, humidity, light level, system power level, aging of the measurement systems, and other environmental factors or changes. Therefore, the measurement devices used in dispense systems can be affected. For example, over time, the zero offset error value of the measurement may drift away from an initially calculated value (hereinafter, “zero offset drift”). Users of these measurement devices may recalculate the zero offset error to account for the zero offset drift. Typically zero offset error calculation is done by the measurement device, but it needs an input that indicates that the actual flow rate is zero. This indication may be a button/switch that the user activates when the flow rate is known to be zero. This process is inefficient and subject to human errors.
Therefore, there is a need for a measurement device for verifying the actual dispensed volume of a dispense system. There is also a need for a system and method for automatically correcting the zero offset drift for the measurement device.